Power and ground routing of integrated circuit devices with improved IR drop and chip performance

ABSTRACT

An integrated circuit chip includes a semiconductor substrate having thereon a plurality of inter-metal dielectric (IMD) layers and a plurality of first conductive layers embedded in respective the plurality of IMD layers, wherein the first conductive layers comprise copper; a first passivation layer overlying the plurality of IMD layers and the plurality of first conductive layers; a plurality of first power/ground mesh wiring lines, formed in a second conductive layer overlying the first passivation layer, for distributing power signal or ground signal, wherein the second conductive layer comprise aluminum; and a second passivation layer covering the second conductive layer and the first passivation layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.12/052,735 filed Mar. 21, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the integrated circuit power andground routing and, more particularly, to a novel power and groundrouting of integrated circuit (IC) chip devices that utilizes aluminumlayer to form power or ground lines for distributing power across the ICfrom an off chip source to various blocks within the IC, therebyreducing the IR drop (or voltage drop) of the integrated circuit chipdevices and improving the chip performance.

2. Description of the Prior Art

In the processes for designing a large-scale integrated semiconductorcircuit device, respective blocks of the device are generally designedin parallel to complement device characteristics with one another.During the designing the large-scale device, the building-block type ofmethod is utilized, in which the circuit of the device is divided into aplurality of circuit blocks and each of the circuit blocks is thusdesigned at the same time. The overall design of the device is thencarried out by integrating these constituent blocks.

An integrated circuit (IC) usually has a larger number of circuit blocksand multiple levels of conductors are used to distribute power andsignals from off the IC to the circuit blocks within the IC, between thecircuit blocks, and between cells within each circuit block.

The conductors are formed by lithographically patterning a layer ofconductive material to form conductive lines as viewed from above the ICsubstrate. The conductive layers with conductive lines formed thereinare isolated by an insulating layer so that lines of one layer whichcross another layer do not physically or electrically contact eachother. When it is desired to electrically connect a conductive lineformed in one layer to a conductive line formed in another layer, aconductive via is formed extending through the insulating layer betweenthe two conductors.

The conductive layers typically have different sheet resistances, withthe lowest level (layer 1 or M1) having the highest sheet resistance andthe highest level having the lowest sheet resistance. This is due totechnological processing constraints such as smaller thickness at thelower layers. The different sheet resistances have influenced routing,for example, with the higher sheet resistance, lower layers generallybeing used to make connections which are relatively close (e.g. withincells or blocks) while the higher level, lower sheet resistance layersare used to make longer connections, such as between points in differentblocks.

FIG. 1 is an enlarged top view of a conventional IC chip device with sixlevels of copper metal layers, wherein merely a small part of aparticular circuit block of the IC chip device is illustrated for thesake of simplicity. As shown in FIG. 1, a circuit block 10 has power(V_(DD)) ring 12 and ground (V_(SS)) ring 14 disposed along itsperimeter. The power ring 12 and ground ring 14 are either formed in thesixth-level metal layer (hereinafter M6) or the copper metal layer thatis one level lower than M6, i.e., M5. By way of example, the power ring12 is formed in M6, while the ground ring 14 is formed in M5. In suchcase, some of the other lower levels of copper metal layers, forexample, from the second-level copper metal layer, i.e., M2, to thefourth-level copper metal layer, i.e., M4, may be used for signalrouting.

Within a center region of the circuit block 10 that is surrounded by thepower ring and ground ring, a so-called “mesh” interconnection network20 is provided. The mesh interconnection network 20 consists of aplurality of substantially orthogonal horizontal lines 22 andlongitudinal lines 24. Through the mesh interconnection network 20 andrespective via stacks 32 and 34, the power or ground signals areprovided from respective power or ground rings to the cell level devicessuch as transistors or regions which are fabricated in or on the mainsurface of the semiconductor substrate (not shown) and are not equallyspaced from the ring. The horizontal lines 22 and longitudinal lines 24of the mesh interconnection network 20 are respectively formed in eitherM5 or M6 in this exemplary case.

In addition, in current copper processes, a layer of aluminum disposedunder a passivation layer is mainly used to provide a bondableinterface, an aluminum bond pad, atop a copper bond pad formed in thetopmost copper metal layer of the integrated circuit chip in order toprevent oxidation of the underlying copper bond pad. In some cases, thelayer of aluminum disposed under the passivation layer may be used toform so-called re-distributed layer (RDL) to re-distribute the aluminumbond pad to other location primarily for flip-chip applications.

The prior art approach of using the topmost two levels of the coppermetal layers, i.e., M5 and M6, for power and ground routing induces thatthe voltage drop (or IR drop) is unavoidably high. This is partly due tothat M5 and M6 have different thicknesses and different sheetresistances (Rs). Typically, M5 is much thinner than M6, and thus has ahigher sheet resistance (roughly about two times of the sheet resistanceof M6).

Therefore, there is a strong need in this industry to provide animproved power and ground routing for the integrated circuit chipdevices that is capable of reducing the IR drop, thus improving the chipperformance.

SUMMARY OF THE INVENTION

It is one object of the invention to provide an improved power andground routing for the integrated circuit chip devices that is capableof reducing the IR drop and improving the chip performance.

It is another object of the invention to provide an integrated circuitchip device that utilizes aluminum layer over passivation to form poweror ground lines, thereby reducing the IR drop of the integrated circuitchip device and improving the performance thereof.

According to the claimed invention, an integrated circuit chip includesa semiconductor substrate having thereon a plurality of inter-metaldielectric (IMD) layers and a plurality of first conductive layersembedded in respective the plurality of IMD layers, wherein the firstconductive layers comprise copper; a first passivation layer overlyingthe plurality of IMD layers and the plurality of first conductivelayers; a plurality of first power/ground mesh wiring lines, formed in asecond conductive layer overlying the first passivation layer, fordistributing power signal or ground signal, wherein the secondconductive layer comprise aluminum; and a second passivation layercovering the second conductive layer and the first passivation layer.

From one aspect of this invention, an integrated circuit chip includes asemiconductor substrate having thereon a plurality of inter-metaldielectric (IMD) layers and a plurality of first conductive layersembedded in respective the plurality of IMD layers, wherein the firstconductive layers comprise copper; a first passivation layer overlyingthe plurality of IMD layers and the plurality of first conductivelayers; a first power/ground ring, formed in a second conductive layeroverlying the first passivation layer, for distributing power signal orground signal, wherein the second conductive layer comprise aluminum;and a second passivation layer covering the second conductive layer andthe first passivation layer.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings:

FIG. 1 is an enlarged top view of a conventional integrated circuit chipdevice with six levels of copper metal layers;

FIG. 2 is a schematic, cross-sectional diagram illustrating a germaneportion of the exemplary integrated circuit chip that is fabricated withsix levels of copper metal layers in accordance with one preferredembodiment of this invention;

FIG. 3 is a schematic, cross-sectional diagram illustrating the secondpreferred embodiment of the invention; and

FIG. 4 is a schematic diagram showing the layout in accordance with thesecond preferred embodiment of this invention.

DETAILED DESCRIPTION

The invention pertains to a novel power and ground routing capable ofimproving the performance of the integrated circuit chip. The inventionutilizes a layer of aluminum in a passivation layer of the integratedcircuit chip to form the power or ground ring and/or meshinterconnection network instead of the copper metal layer (Mn−1) that isjust one level lower than the topmost copper metal layer (Mn) of theintegrated circuit chip. Therefore, one of the topmost two levels of thecopper metal layers that used to be formed into power and ground ringsand mesh interconnection network can thus be eliminated or be spared forsignal routing. Alternatively, the replaced Mn−1 copper layer can beskipped for saving photomask and cost. The invention can increase signalrouting source and increase the flexibility of placement and routing.

The preferred embodiments of this invention will now be explained withthe accompanying figures. Throughout the specification and drawings, thesymbol “Mn” refers to the topmost level of the copper metal layersfabricated in the integrated circuit chip, while “Mn−1” refers to thecopper metal layer that is just one level lower than the topmost coppermetal layer and so on, wherein, preferably, n ranges between 5 and 8 butnot limited thereto. The symbol “V” refers to the via plug between twoadjacent conductive metal layers. For example, V5 refers to the via pluginterconnecting M5 to M6.

FIG. 2 is a schematic, cross-sectional diagram illustrating a germaneportion of the exemplary integrated circuit chip 1 a that is fabricatedwith six levels of copper metal layers (M1-M6) in accordance with onepreferred embodiment of this invention. As shown in FIG. 2, theexemplary integrated circuit chip 1 a includes a semiconductor substrate100 such as a silicon substrate, a silicon-on-insulator (SOI) substrate,SiGe substrate or the like. A plurality of inter-metal dielectric (IMD)layers 110-132 are deposited over the semiconductor substrate 100.Circuit elements 101 such as transistors, capacitors or memory cells arefabricated on the main surface of the semiconductor substrate 100. TheIMD layers 110-132 may be formed of low dielectric constant (low-k)materials or ultra low-k materials, but not limited thereto. The IMDlayers 110-132 may comprise conventional dielectric layer such assilicon oxide, silicon nitride, silicon carbide or silicon oxy-nitride.The low-k or ultra low-k materials described herein may be eitherorganic (e.g., SILK) or inorganic (e.g., HSQ) and may be of a porous ornon-porous nature.

According to this invention, M1-M6 and respective vias V1˜V5 arefabricated using copper damascene processes or dual damascene processes,which are well known in the art and are thus not discussed further. Thefirst level of the copper metal layers, i.e., M1 is fabricated in theIMD layer 112. A contact plug 220, typically tungsten plug, is formed inthe IMD layer 110 to interconnect M1 to the circuit elements 101. Thesecond level of the copper metal layers, i.e., M2 is fabricated in theIMD layer 116. A via plug V1, typically damascened copper plugintegrated with M2, is formed in the IMD layer 114 to interconnect M1 toM2. The third level of the copper metal layers, i.e., M3 is fabricatedin the IMD layer 120. A via plug V2 is formed in the IMD layer 118 tointerconnect M2 to M3. The fourth level of the copper metal layers,i.e., M4 is fabricated in the IMD layer 124. A via plug V3 is formed inthe IMD layer 122 to interconnect M3 to M4. The fifth level of thecopper metal layers, i.e., M5 is fabricated in the IMD layer 124. A viaplug V4 is formed in the IMD layer 122 to interconnect M4 to M5. Thetopmost level of the copper metal layers, i.e., M6 is fabricated in theIMD layer 132. A via plug V5 is formed in the IMD layer 130 tointerconnect M5 to M6.

A first passivation layer 140 is deposited on the IMD layer 132 andcovers the exposed M6 layer. The first passivation layer 140 maycomprise silicon oxide, silicon nitride, polyimide or other suitablematerials.

The integrated circuit chip 1 a further comprises a bonding area 300. Analuminum pad 302 is formed on the first passivatioin layer 140 withinthe bonding area 300. The aluminum pad 302 is electrically connectedwith the underlying copper pad 304 that is formed in M6 layer throughvia 306. This aluminum pad 302 prevents oxidation of the underlyingcopper pad 304. The aluminum pad 302 may be part of a power or groundring surrounding a circuit block of the integrated circuit chip 1 a.

The aluminum pad 302 is covered with a second passivation layer 142. Thesecond passivation layer 142 may comprise silicon oxide, siliconnitride, polyimide or other suitable materials. An opening or window 308is provided in the second passivation layer 142 to expose a portion ofthe top surface of the aluminum pad 302. The opening 308 may be formedby conventional lithographic and etching methods.

The integrated circuit chip 1 a depicted in FIG. 2 is fabricated basedon a so-called 1P6M scheme (one polysilicon layer and six copper metallayers). However, this invention is also applicable to otherinterconnection schemes such as 1P3M, 1P4M, 1P5M, 1P7M or 1P8M etc.

As previously described, the topmost level of the copper metal layers,i.e., M6 is much thicker than M5, and thus M5 has a higher sheetresistance (Rs). For example, M6 has a thickness t1 of about 0.85micrometers (line width=0.36 micrometers; Rs=0.0212 Ω/cm2), and M5 has athickness t2 of about 0.29 micrometers (line width=0.18 micrometers;Rs=0.0779 Ω/cm2).

Still referring to FIG. 2, the integrated circuit chip 1 a furthercomprises a power or ground ring 402 that is formed in the aluminumlayer over the first passivation layer 140. The aluminum pad 302 and thealuminum power or ground ring 402 can be formed concurrently. Thethickness t3 of the aluminum power or ground ring 402 is ordinarilyabout 1.45 micrometers, which is much thicker than M6 layer. Preferably,to efficiently distributing power, it is recommended that the line width(L) of the power or ground ring 402 is about 3.0 micrometers with aspacing (S) of about 2.0 micrometers (L/S=3/2). The line width of thealuminum power or ground ring 402 may range between 3 micrometers and 30micrometers.

Since the aluminum power or ground ring 402 is thick, the sheetresistance of the aluminum power or ground ring 402 can be as low asabout 0.0212 Ω/cm2 which is close to M6 layer. The aluminum power orground ring 402 may be electrically connected to the underlying coppertrace line 404 through via 406. According to the preferred embodiment ofthis invention, the via 406 preferably has a dimension of 3 micrometersor 3-micrometer×3-micrometer to efficiently distributing power. Thecopper trace line 404 is formed in M6 layer and may function as part ofthe mesh interconnection network (not explicitly shown) for distributingpower or ground signals to a circuit element 101 by way of, for example,the via stack 502.

The mesh interconnection network, as previously mentioned, includes aplurality of orthogonal horizontal trace lines and longitudinal tracelines across the circuit block. According to the preferred embodiment,the aluminum layer over the passivation layer 140 may be utilized todefine either the horizontal trace lines or longitudinal trace lines ofthe mesh interconnection network.

It is one kernel feature of this invention that the power or groundrings for distributing power or ground signals to a circuit block of theintegrated circuit chip 1 a are formed merely in the topmost level ofthe copper metal layers and in the aluminum layer over the passivationlayer 140. The aluminum layer over the passivation layer 140 is not onlyutilized to be a RDL for flip-chip or bump applications, but also isfurther utilized to form the power or ground signal routing. By doingthis, M5 layer can be eliminated or be spared for flexible signalrouting. The sheet resistance of the Al layer over the passivation 140is much lower than M5 layer; thereby the IR drop is reduced.

FIG. 3 is a schematic, cross-sectional diagram illustrating the secondpreferred embodiment of the invention, wherein the same numeralsdesignate like elements, layers or regions with the similar material andfunction. As shown in FIG. 3, likewise, the integrated circuit chip 1 bcomprises a semiconductor substrate 100. Circuit elements (notexplicitly shown in FIG. 3) such as transistors, capacitors or memorycells are formed on the semiconductor substrate 100. A number ofinter-metal dielectric (IMD) layers are deposited over the semiconductorsubstrate 100. For the sake of simplicity, only IMD layers 128-132 areshown. A first passivatioin layer 140 is deposited on the IMD layer 132and covers the exposed Mn layer.

The integrated circuit chip 1 b comprises n layers of copper metalinterconnection (M1-Mn) and respective vias (V₁-Vn_(n−1)) which arefabricated using copper damascene processes or dual damascene processes,which are well known in the art and are thus not discussed further. Apower/ground ring 502 is formed in combination with the Al layer and theMn layer. A power/ground ring 602 is formed in the Mn−1 layer. The IRdrop is reduced by parallel connecting the Al layer 504 with theunderlying Mn layer 508 through the Al via 506. By doing this, the sheetresistance of the power/ground ring 502 is decreased.

FIG. 4 is a schematic diagram showing the layout in accordance with thesecond preferred embodiment of this invention, wherein the same numeralsdesignate like elements, layers or regions with similar material andfunction. As shown in FIG. 4, an integrated circuit chip 1 c comprises aground ring 508 a for distributing V_(SS) signal and a power ring 508 bfor distributing V_(DD) signal. The parallel ground ring 508 a and thepower ring 508 b are both formed in the Mn layer, i.e., the topmostcopper metal layer of the integrated circuit chip 1 c.

Two exemplary tracing lines 702 and 802 of a mesh interconnectionnetwork, which are orthogonal to the ground ring 508 a and the powerring 508 b, are formed in the Mn−1 layer. The orthogonal tracing line702 is electrically connected to the overlying ground ring 508 a throughvia 706, which is formed between Mn−1 layer and Mn layer. The orthogonaltracing line 802 is electrically connected to the overlying power ring508 b through via 806, which is formed between Mn−1 layer and Mn layer.

Aluminum wiring lines 504 a is deposed right above and parallel toground ring 508 a; and aluminum wiring lines 504 a is connected toground ring 508 a through via 506 a. Aluminum wiring lines 504 b isdeposed right above and parallel to power ring 508 b; and aluminumwiring lines 504 b is connected to power ring 508 b through via 506 b.Preferably, the line width of the aluminum wiring lines 504 a and 504 branges between 3 micrometers and 30 micrometers with a spacing of about20 micrometers. Preferably, the vias 506 a and 506 b have a dimension of3-micrometer×3-micrometer, and the spacing between two adjacent vias 506a is about 3 micrometers. A first passivation layer (not explicitlyshown in FIG. 4) is interposed between the aluminum wiring lines and thepower/ground ring. A second passivation layer such as silicon nitride orpolyimide covers the aluminum wiring lines 504 a and 504 b and the firstpassivation layer.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. An integrated circuit chip comprising: a semiconductor substratehaving thereon a plurality of inter-metal dielectric (IMD) layers and aplurality of first conductive layers embedded in respective saidplurality of IMD layers, wherein said first conductive layers comprisecopper; a first passivation layer overlying said plurality of IMD layersand said plurality of first conductive layers; a plurality of firstpower/ground mesh wiring lines, formed in a second conductive layeroverlying said first passivation layer, for distributing power signal orground signal, wherein said second conductive layer comprise aluminum;and a second passivation layer covering said second conductive layer andsaid first passivation layer.
 2. The integrated circuit chip of claim 1,wherein said integrated circuit chip further comprises: a plurality ofsecond power/ground mesh wiring lines, formed in a topmost layer of saidplurality of first conductive layers, for distributing power signal orground signal; wherein said second power/ground mesh wiring linescomprise a plurality of horizontal trace lines or longitudinal tracelines.
 3. The integrated circuit chip of claim 2 wherein said pluralityof first power/ground mesh wring line has a thickness that is greaterthan that of said second power/ground mesh wiring line.
 4. Theintegrated circuit chip of claim 1 wherein said first power/ground meshwiring lines comprise a plurality of horizontal trace lines orlongitudinal trace lines.
 5. The integrated circuit chip of claim 1,wherein said integrated circuit chip further comprises: a firstpower/ground ring formed in said second conductive layer.
 6. Theintegrated circuit chip of claim 1, wherein said integrated circuit chipfurther comprises: a second power/ground ring formed in a topmost layerof said plurality of first conductive layers.
 7. An integrated circuitchip comprising: a semiconductor substrate having thereon a plurality ofinter-metal dielectric (IMD) layers and a plurality of first conductivelayers embedded in respective said plurality of IMD layers, wherein saidfirst conductive layers comprise copper; a first passivation layeroverlying said plurality of IMD layers and said plurality of firstconductive layers; a first power/ground ring, formed in a secondconductive layer overlying said first passivation layer, fordistributing power signal or ground signal, wherein said secondconductive layer comprise aluminum; and a second passivation layercovering said second conductive layer and said first passivation layer.8. The integrated circuit chip of claim 7, wherein said integratedcircuit chip further comprises: a second power/ground ring, formed in atopmost layer of said plurality of first conductive layers, fordistributing power signal or ground signal.
 9. The integrated circuitchip of claim 8 wherein said first power/ground ring has a thicknessthat is greater than that of said second power/ground ring.
 10. Theintegrated circuit chip of claim 7, wherein said integrated circuit chipfurther comprises: a plurality of first power/ground mesh wiring lines,formed in said second conductive layer, for distributing power signal orground signal; wherein said plurality of first power/ground mesh wiringlines comprise a plurality of horizontal trace lines or longitudinaltrace lines.
 11. The integrated circuit chip of claim 7, wherein saidintegrated circuit chip further comprises: a plurality of secondpower/ground mesh wiring lines, formed in a topmost layer of saidplurality of first conductive layers, for distributing power signal orground signal; wherein said plurality of second power/ground mesh wiringlines comprise a plurality of horizontal trace lines or longitudinaltrace lines.